Based on the press room seating charts, it looks to be someone from the Wall Street Journal. It doesn't look like Susan Davis or Sara Murray, two of the Journal's women Washington reporters that we'd recognize, and it's obviously not White House correspondent John McKinnon. Anyone? It's not like there are that many women in that room, ever. This shouldn't be so hard.
(Update 2: A tipster writes: "I'm pretty sure it's Laura Meckler at WSJ. Could be! The one pic we can find looks similar!)
Update the Third: It's almost surely Laura Meckler, and she's PREGNANT. So lay off. Pregnant ladies just need sleep, sometimes.